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Beirut has been experiencing some of the worst street fighting and sectarian clashes since Lebanon’s 15-year civil war.

Richard Engel, NBC News’ Chief Foreign Correspondent, explains what sparked the outbreak of violence and what the underlying issues are.

What does Hezbollah want?
In a word, Hezbollah wants power.

The long-simmering crisis in Lebanon boiled when the government tried to fire the director of security at Beirut's international airport. On the surface it doesn't seem like a major incident. But Beirut's airport has long been a key Hezbollah supply line, a gateway for weapons, funding and personnel, mainly from Iran.

During the 2006 war between Israel and Hezbollah, Israeli jets quickly targeted the airport to disrupt this supply line. The Lebanese government also called to dismantle a private telephone network of fiber-optic lines that Hezbollah uses to communicate with its fighters. The phone lines – harder to monitor than cell phones – were key to Hezbollah's ability to wage war against Israel.

Hezbollah reacted decisively to the government's demands, declaring that control of airport security and its phone network are vital to the group's existence. Hezbollah maintains that its weapons (everything from rockets and guns to bunkers and a telecoms network) are necessary to protect Lebanon from Israel. Hezbollah was pushed, and pushed back hard.

Why did Hezbollah take over most of Beirut?
Hezbollah wants to discredit the government and show how much power and control the Iranian-backed group truly exerts in Lebanon. Hezbollah wants to prove that it is stronger than the government, which for now it seems to be.

Hezbollah also moved to quiet a rival political party, the Future Movement, which is allied to the government. Hezbollah members see the Future Movement, and the government in general, as a group of rich “upstarts” who talk, insult their organization, but do little else.

Hezbollah finds them annoying. At the start of the outbreak, Hezbollah gunmen moved from their stronghold in southern Beirut and quickly took over the Future Movement's offices and closed and burned its television station. The upstarts were silenced.

While some Lebanese, and clearly the government, accuse Hezbollah of occupying Beirut, Hezbollah believes it is showing the world, and the Lebanese people, who holds the real power in the country. It wants to show that the government (which always claims to be backed by a majority in Lebanon) is in fact a small, unpopular, weak group of pro-American, pro-Israeli officials unable to even control the capital. It was a power play.

So what happens next?
Watch the small parties. Hezbollah and the government are only two of 18 political factions in Lebanon, most of them armed. There are militant Christian groups, Palestinian radicals, al-Qaida, Druze militias and even armed bands of Marxists still operating in Lebanon.

These groups could, as they have in the past, start fighting among themselves. If that happens, Hezbollah could sit back and position itself as the “savior” of Lebanon, claiming to be the only party strong enough to stabilize this troubled little nation. Hezbollah could say, “We are the only ones who can stop a civil war.” The government will say, “But you caused it.”

What is the army doing?
The army is for now riding the tide, which seems to be going with Hezbollah. The army has not intervened and mans checkpoints as Hezbollah men takeover positions. The army has not been willing to stop Hezbollah, or even tried. The army's loyalties are split between the government and Hezbollah. Instead of collapsing, the army decided not to back any side and watch what happens.

Can diplomacy work?
The conflict in Lebanon is as much driven by outside interests as internal rivalries for power. Iran and Syria back Hezbollah. The United States (and to a degree Israel) back the Lebanese government.

The Arab powers – mainly Syria, Egypt, Saudi Arabia, and Jordan – worry that if the government in Beirut falls, it will be seen as having been toppled by Iran. The Sunni Arab states do not want Iran's influence to spread any further in the Middle East, especially as Iran's power has grown after the U.S. invasion of Iraq. There are calls for urgent meetings of Arab foreign ministers. They meet often. Little gets done. Meanwhile, Lebanon is sinking.